This invention relates generally to a printer, and particularly to a thermal printer wherein electrical energy supplied to a heating element for generating thermal energy is applied to a thermally sensitive paper for developing print characters thereon.
Platens in thermal printers have generally been formed from plastic or fubber material. In thermal printers, printing is achieved by positioning a thermal print head next to a thermal print paper against a platen. Columns of characters are printed by displacing the thermal head across paper in a serial printer. Rows of characters are formed by advancing the paper across the thermal print head in a parallel type printer.
In order to be effective, a platen for a thermal printer must satisfy the following requirements. First, the platen must provide consistently good printing quality, and must not impart any shading differences among the letters in a printed line. Second, the platen must reduce friction between the thermal head and the platen surface to permit smooth reciprocal motion of the print head. This is required even if thermal paper is not in position between the print head and the platen surface. Third, the platen surface must not impair the durability of the thermal head or wear of the other mechanical parts of the printer. To date, the conventional unitary practical rubber platens have not satisfactorily fulfilled these requirements. Attempts to overcome the disadvantages have been made, for example by utilizing a platen formed from a relatively soft rubber so that it is more easily deformed. Additional efforts include increasing the force of a compression spring for increasing the pressure of the platen. In addition, attempts have been made to increase the power consumption to the thermal head for darkening the printing for improving uniformity of the print.
Although these methods have succeeded in reducing differences in contrast of the printing, they do not provide a satisfactory solution. Specifically, if the load on the thermal head is increased, this increases the power consumed in order to reciprocate the print head across the print paper. This also results in heavier wear of the protective layer on the thermal head and a reduction in the useful life from the increased pressure. This increased wear tends to generate noise due to the increased friction between the drive shaft and the holder resulting in permanent deformation of a rubber platen.
Accordingly, it is desirable to provide a platen for a thermal printer which overcomes many of these drawbacks and provides a highly durable thermal printer of superior printing quality at low power consumption.